Transmission belts comprising a cord with at least two fused yarns

ABSTRACT

The invention pertains to a transmission belt comprising a cord, a rubber or thermoplastic matrix, and an adhesion material which is able to adhere the cord to the rubber or thermoplastic matrix, characterized in that the cord is made of at least two yarns, the first being a yarn with a melting or decomposition point T 1  and the second being a yam with a melting point T 2 , wherein T 1 &gt;T 2  and the ratio of the linear density of the first yarn to the linear density of the second yam is between 1,000:1 and 1:1, wherein the second yarn is fused to the first yarn. The invention also pertains to a method in which the first and the second yarn are intertwined and then heated at a temperature between T 1  and T 2 , with the heating step being integrated with or followed by a step wherein the cord is subjected to a dipping treatment with a rubber adhesion material and to a method of making transmission belts using said cords.

[0001] The invention pertains to a transmission belt comprising a cord with at least two fused yarns, to a method of manufacturing the cord, and to a method of manufacturing the transmission belt.

[0002] Cords for reinforcing rubber articles are known in the art. A cord for that purpose comprising at least one high-modulus yarn and at least one low-modulus yarn is disclosed in WO 97/06297. The yarns of these cords may be twisted together and can be dipped with a rubber adhesive material. The low-modulus yarn is primarily added as a process aid to enable high-modulus yarns to be used in mould curing processes. By this method transmission belts can be produced; however, during the processing of such belts the mechanical properties of the cord tend to deteriorate.

[0003] High bundle cohesion is essential to avoid fraying when the belts get their final shape as they are cut out of a rubber composite slab. In order to produce a clean cut, all the filaments in the yam bundle have to be secured firmly together in the cutting plane. If they are not held in place, the applied cutting force can move filaments out of the cutting plane, causing filaments to be cut at different lengths (the effect called “fraying”). In order to meet the quality standards set by the belt industry, fraying must be kept to an absolute minimum, not for optical reasons only but also to prevent a possible failure initiation. For that reason both aramid and polyester cords are usually pre-dipped with a solvent-based MDI (diphenylmethane-4,4-diisocyanate) pre-dip to obtain high filament coherence. The pre-dipping with MDI results in a rather stiff cord with excellent cutting behavior, though at the cost of poor strength efficiency after the dipping process (10 to 20% strength loss compared to standard “soft-dipping”). Moreover, it was found that stiff-dipped p-aramid cords suffer from severe strength loss after handling and vulcanization. This strength loss is proportional to the stiffness (i.e. the degree of impregnation) and is presumably induced by kink bands while buckling the stiff aramid cords. This phenomenon resulting in loss of strength while handling or processing stiff-dipped cords is called “handling resistance” or “handleability”.

[0004] It is an object of the present invention to manufacture transmission belt using cords with high bundle cohesion, having high strength efficiency and good adhesion while maintaining good handling resistance. This is particularly important for good cuttability behavior while producing open edge transmission belts.

[0005] The invention pertains to a transmission belt comprising a cord, a rubber or thermoplastic matrix, and an adhesion material which is able to adhere the cord to the rubber or thermoplastic matrix, characterized in that the cord is made of at least two yarns, the first being a yarn with a melting or decomposition point T₁ and the second being a yarn with a melting point T₂, wherein T₁>T₂ and the ratio of the linear density of the first yarn to the linear density of the second yarn is between 1,000:1 and 1:1, wherein the second yarn is fused to the first yarn.

[0006] Preferably, the ratio of the linear density of the first yarn to the linear density of the second yarn is between 100:1 and 4:1, and more preferably between 35:1 and 15:1.

[0007] For use in transmission belts the cord of the instant invention must contain a rubber or thermoplastic matrix adhesion material. Examples are chloroprene rubber (CR), hydrogenated butadiene acrylonitrile rubber (HNBR), alkylated chlorosulfonated polyethylene (ACSM), ethylene propylenediene rubber (EPDM), polyurethane (PU).

[0008] In order to ensure that in the transmission belt there is good adhesion of the cords to the matrix material of the belt, it is required to coat the cords with an adhesive. Therefore, the cords are treated with an adhesive system prior to being contacted with the matrix material. Preferably, the cords are provided with a first adhesive coating before they are treated with the rubber or the thermoplastic matrix adhesive material. Highly suitable first adhesive coatings include epoxy compounds, polymeric methyl diphenyl diisocyanate (e.g., Voranate® ex DOW), and polyurethanes having ionic groups.

[0009] The adhesive system also offers several options. Highly suitable for use in the case of, e.g., poly(para-phenylene terephthalamide) are a resorcinol/formaldehyde/latex (RFL) system and Chemosil® (ex Henkel). In the case of, e.g., glass, use may be made of a silane compound.

[0010] Preferred rubber adhesion materials are the ones based on recorcinol/form-aldehyde/latex systems.

[0011] The cord is particularly suitable for use in open-edge transmission belts, yet if the rubber adhesion treatment is omitted, the obtained cord is also suitable for use in other applications where high bundle cohesion is desired, such as in ropes, cables, hoses, and the like.

[0012] Highly suitable materials for yams with relatively high melting or decomposition points (T₁) include aromatic polyamides (aramid), such as poly(para-phenylene terephthalamide). Over the years these materials have proved especially suitable for use in composites. Aramid is frequently employed in composites with a rubber matrix among others. Other examples of appropriate materials are polyesters.

[0013] As suitable materials for yarns with relatively low melting points (T₂) may be mentioned polyesters, polyamides, polyolefins, elastodienes, elastanes, thermoplastic vulcanizates, and chlorofibres.

[0014] Some of these materials have been used in composites such as tires and drive belts for many years. Other examples of suitable materials are polyolefins, cellulose, acetate, acrylic material, and vinylal. The preferred yarn for transmission belt application is Perlon yarn 13-96 dtex (PA6 POY, melting point ±220° C.).

[0015] The method of manufacturing the cord of this invention comprises the steps of intertwining the first and the second yarn and then heating the intertwined cord at a temperature between T₁ and T₂, wherein the heating step is integrated with or followed by a step wherein the cord is subjected to a dipping treatment with a rubber adhesion material.

[0016] The heating step is performed to fixate the first yarn bundles by melting the second (fusion) yarn. The molten filaments embrace the single plies, thereby interlocking the filaments and holding them in place to enhance their cuttability.

[0017] The dipping treatment in order to prepare the cord for good adhesion to rubber or thermoplastic matrix is a well-known process. Depending on the basic cord yarn, a single- or two-bath dipping process can be used.

[0018] For technical and economical reasons, the fixation (heating) step ideally takes place during the dipping process. By selecting a thermoplastic adhesive with a melting point within the range of temperatures used for the dipping treatment, the heat setting can be combined with the dip-curing steps. By selecting a thermoplastic adhesive with a melting point between 200-250° C., the heat-setting can be combined with the curing step in a conventional dipping process. Integrated RFL dipping and heat setting is the preferred method for the production of aramid cords for transmission belts.

[0019] The method can be applied to any cord construction; however, typical applications are cord constructions with a linear density ranging from 210 to 50,000 dtex. A typical construction for transmission belt application is Twaron®2300 1680 dtex×2 Z190×3 S115 (linear density: 1680×2×3=10080 dtex).

[0020] The distribution of the second (fusion) yarn is controlled by intertwining the fusion yarn according to appropriate twisting schemes and is dependent on the type of cord construction. The twisting scheme and the amount of fusion yarn relative to the first yarn used depend on the desired bundle cohesion and are easily determined by those skilled in the art. Twisting regimens are well-known in the art. The twisting can be carried out with any suitable twisting equipment.

[0021] In order to distribute the adhesive for this cord one can apply several twisting schemes, depending on the complexity of the cord construction. For Twaron® 2300 1680 dtex×2Z190×3S115 construction, for instance, a basic two-step twisting scheme I or a basic three-step scheme II can be used. The distribution of adhesive is controlled by varying the number of feed points and the positions where the fusion yarn is fed into the aramid construction. When using a two-step basic twisting scheme, there are 6 feeding positions, with 12 different twisting scheme possibilities in total. If a three-step basic twisting scheme is used, there are 12 feeding positions, with 72 different twisting scheme possibilities in total.

[0022]

[0023] The preferred method of twisting a typical construction for transmission belt application is given in Scheme III.

[0024] The invention is further illustrated by the following examples.

EXAMPLE 1 Dipping Conditions

[0025] For a typical aramid construction for transmission belt application the following dipping conditions are chosen. Two-bath procedure: Pre dipping conditions. dip: T03 (2%) GE100 epoxide oven 1 residence time: 120 sec temperature: 150° C. tension: 25 N RFL dipping conditions dip: VP latex A11 (25%) oven 2 residence time: 120 sec temperature: 150° C. tension: 25 N oven 3 residence time:  60 sec temperature: 235° C. tension: 25 N One-bath procedure: RFL dipping conditions dip: VP latex A11 (25%) oven 1 residence time: 120 sec temperature: 150° C. tension: 25 N oven 2 residence time:  60 sec temperature: 235° C. tension: 25 N

[0026] The dip treatment was carried out on a Litzler laboratory dipping unit according to the known art of the two-bath—three-oven dipping procedure. The greige cord was reeled off at position a. The GE-100 pre-dip was applied by submerging the cord in a dip container at position c and subsequently curing it in oven 1. The RFL dip was applied at position g and was subsequently dried and cured in oven 2 and oven 3, respectively. At position h, the dipped cord was wound on a spool. The dipping speed and the tension were maintained at a constant level by the control units c, d, f, and g.

[0027] Preparation of T03 (2%) GE100 e

[0028] To 978.2 g of demin (demineralized) water in a polyethylene bottle was added 0.5 g of piperazine, and the mixture was stirred with a glass rod till the solids were dissolved. Under stirring with the glass rod 1.3 g of Aerosol™ OT 75% (surfactant dioctyl sodium sulfosuccinate in 6% ethanol and 19% water) (Chemical Corporation Pittsburgh, Pa., USA) were added, and thereafter 20.0 g of GE-100 epoxide (mixture of di- and trifunctional epoxide on the basis of glycidyl glycerin ether (Raschig AG, Ludwigshafen, Germany) were added. The mixture was stirred mechanically during 1 min and the preparation was matured for 12 h at room temperature.

[0029] The storage life of this dip was five days in a refrigerator between 5-10° C.

[0030] Formulation RFL Dip A11

[0031] Preparation:

[0032] A mixture of 275.3 g of demin water, 12.9 g of ammoniumhydroxide 25%, and 69.4 g of Penacolite® R50 50% (recorcinol-formaldehyde polymer resin solution) (Chemical Corporation Pittsburgh, Pa., USA) was added to Pliocord® VP106 (aqueous dispersion of a vinylpyriden-styrene-butadiene terpolymer (40%)) (Goodyear Chemicals, Europe, Les Ulis, France) and stirred during 3 min. A mixture of 23.1 g of formaldehyde 37% and 110.6 g of demin water was added and stirred for another 3 min. The dip was matured for 12 h at room temperature.

[0033] The storage life is five days in a refrigerator between 5-10C.

EXAMPLE 2

[0034] The properties of the cords were measured as specified in document IN97/7180, “Standard methods of testing Twaron filament yarns and cords”, version 4, 01-01-1997 of Twaron Products. For tensile test methods reference is made to ASTM D885—“Standard Test Methods for Tire cords, Tire Cord Fabrics, and Industrial Filament Yarns” —and EN 12562—“Para-aramid multi filament yarns—Test methods”.

[0035] The mechanical properties are listed in Table 1, comparing:several dip-treated aramid cords samples.

[0036] Stiff Dipped:

[0037] a) MDI (2.5%)/A11 (20%): aramid cord dip-treated with pre-dip-containing 2.5% MDI and RFL dip-treatment A11 (20%).

[0038] b) MDI (5%)/A11 (20%): aramid cord dip-treated with pre-dip-containing 5% MDI and RFL dip-treatment A11 (20%).

[0039] c) MDI (10%)/A11 (20%): aramid cord dip-treated with pre-dip-containing 10% MDI and RFL dip-treatment A11 (20%).

[0040] Soft Dipped:

[0041] d) T03 (0.5%)/A11 (25%): newly developed aramid cord with thermoplastic impregnation treated with pre-dip-containing 0.5% GE100 epoxide and RFL dip-treatment A11 (25%).

[0042] e) T03 (0-5%)/A11 (25%): aramid cord dip-treated with pre-dip-containing 0.5% GE100 epoxide and RFL dip-treatment A11 (25%).

[0043] f) T03 (1 %)/A11 (25%): newly developed aramid cord with thermoplastic impregnation treated with pre-dip-containing 1 % GE100 epoxide and RFL dip-treatment A11 (25%).

[0044] g) T03 (1 %)/A11 (25%): aramid cord dip-treated with pre-dip-containing 1 % GE100 epoxide and RFL dip-treatment A11 (25%).

[0045] h) T03 (2%)/A11 (25%): newly developed aramid cord with thermoplastic impregnation treated with pre-dip-containing 2% GE100 epoxide and RFL dip-treatment A11 (25%).

[0046] i) T03 (2%)/A11 (25%): aramid cord dip-treated with pre-dip-containing 2% GE100 epoxide and RFL dip-treatment A11 (25%).

[0047] The following properties were measured according to internal procedures.

[0048] Dip Eff.-Absolute

[0049] Dip efficiency absolute=percentage retained strength of cord after dip treatment relative to the absolute breaking strength of the untreated greige cord.

[0050] Calculation: $\frac{{Absolute}\quad {breaking}\quad {strength}\quad {dipped}\quad {{cord}(N)}}{{Absolute}\quad {breaking}\quad {strength}\quad {greige}\quad {{cord}(N)}} \times 100\quad (\%)$

[0051] Strap Peel Force

[0052] Adhesion test according ASTM D4393 using

[0053] a) CR compound=chloroprene rubber compound and

[0054] b) NR compound=natural rubber compound Dunlop 5320.

[0055] Handle Ret. Strength

[0056] Handleability retained strength=absolute retained strength after vulcanization and manual handling.

[0057] Handleability retained strength is measured after cords are extracted from a vulcanized rubber composite. Since this procedure not only includes a vulcanization process but also a portion of severe manual handling (bending, buckling and kinking), the retained strength is also referred to as the ability to handle resistance or “handleability”.

[0058] Handleability Retained Strength Test Procedure:

[0059] Cords are embedded between two layers of Dunlop 5320 NR rubber compound of 1-2 mm thickness in a form of 440 mm length, 190 mm width. The longitudinal cord layer (pitch 10 ends per inch (2.54 cm)) is maintained in the central position while the composite is preformed and vulcanized in a mould at 160° C. during 20 to 30 min. After cooling, the obtained slab is divided into straps of 1-inch (2.54 cm) width. From each strap, individual cord samples are extracted by hand. While one end of the strap is clamped in a vice, incisions between the cords are made at the other end of the strap. The cords are then separated by being tom at an angle >90° away from the strap. The retained tensile strength of at least six extracted cords is measured (omitting the outer cords of each strap).

[0060] Handle Perc. Ret. Strength

[0061] Handleability percentage retained strength=percentage of retained strength after vulcanization and manual handling relative to the absolute breaking strength of the dip treated cord. $\frac{\begin{matrix} {{{Absolute}\quad {retained}\quad {strength}\quad {after}\quad {vulcanization}}\quad} \\ {{and}\quad {manual}\quad {handling}\quad (N)} \end{matrix}}{\text{Absolute}\quad {breaking}\quad {strength}\quad {of}\quad {dipped}\quad {cord}\quad (N)} \times 100\quad (\%)$

TABLE 1 Tensile properties of Twaron 2300 development constructions. Cord construction Twaron 2300 1680 x2 Z190 x3 S115 Dip treatment stiff dipping soft dipped recipe pre-dip MDI(2.5%) MDI (5%) MDI (10%) T03 (5%) T03 (1%) T03 (2%) Dip conditions recipe RFL dip A11 (20%) A11 20%) A11(20%) A11(25%) A11(25%) A11(25%) Cord sample a b c d e f g h i Description unit {overscore (X)} {overscore (X)} {overscore (X)} {overscore (X)} {overscore (X)} {overscore (X)} {overscore (X)} {overscore (X)} {overscore (X)} Breaking strength N 1615 1643 1650 2061 2000 2003 1978 1796 1885 Elongation at break % 3.8 3.8 3.7 4.3 4.2 4.2 4.2 4.0 4.1 Force at specified N 372 381 392 398 389 393 397 380 397 elongation 1% Force at specified N 779 801 827 876 850 868 868 820 842 elongation 2% Force at specified N 1239 1269 1301 1379 1350 1375 1367 1307 1331 elongation 3% Dip efficieny % 78.8 80.1 80.4 96.8 93.1 94.0 92.3 84.2 88.5 absolute Strap peel force CR compound N/2 cm — — — 194 235 189 235 — — Strap peel force NR compound N/2 cm — — — 222 294 221 287 247 270 Handle.ret strength N 1390 1250 1120 1866 1880 1890 1850 — — Handle.perc.ret % 86.1 76.1 67.9 90.5 94.0 94.4 93.5 — — strength

EXAMPLE 3

[0062] Cord constructions of two-step twisting (BISFA notations):

[0063] A: ((Twaron 2300 1680 dtex×2+PA6 44 dtex)×Z190+(2×(Twaron 2300 1680dtex ×2Z190))) S115.

[0064] B: (2×(Twaron 2300 1680 dtex×2+PA6 44 dtex)×2Z190)+Twaron 2300 1680 dtex ×2Z190) S115.

[0065] C: (Twaron 2300 1680 dtex×2+PA6 44 dtex)×1Z190×3S115.

EXAMPLE 4

[0066] Cord constructions of three-steps twisting (BISFA notations):

[0067] D: ((Twaron 2300 1680 dtex+PA6 44 dtex) Z60+Twaron 2300 1680dtex Z60) Z130+(2×(Twaron 2300 1680 dtex Z60×2Z130)) S115;

[0068] E: (Twaron 2300 1680 dtex+PA6 44 dtex) Z60+Twaron 2300 1680dtex Z60) Z130×3S115;

[0069] F: (Twaron 2300 1680 dtex×2+PA6 44 dtex) Z60×2Z130×3S115. 

1. A transmission belt comprising a cord, a rubber or thermoplastic matrix, and an adhesion material which is able to adhere the cord to the rubber or thermoplastic matrix, characterized in that the cord is made of at least two yarns, the first being a yarn with a melting or decomposition point T₁ and the second being a yarn with a melting point T₂, wherein T₁>T₂ and the ratio of the linear density of the first yarn to the linear density of the second yarn is between 1,000:1 and 1:1, wherein the second yarn is fused to the first yarn.
 2. The transmission belt of claim 1 wherein the yarn with a melting or decomposition point T₁ is an aramid or a polyester yarn.
 3. The transmission belt of claim 1 or 2 wherein the matrix is a rubber matrix and the adhesion material is a recorcinol/formaldehyde/latex system.
 4. A method of manufacturing a cord made of at least two yarns, the first being a yarn with a melting or decomposition point T₁ and the second being a yarn with a melting point T₂, wherein T₁>T₂ and the ratio of the linear density of the first yarn to the linear density of the second yarn is between 1,000:1 and 1:1, wherein the second yarn is fused to the first yarn, characterized in that the first and the second yarn are intertwined and then heated at a temperature between T₁ and T₂, whereby the heating step is integrated with or followed by a step wherein the cord is subjected to a dipping treatment with an adhesion material, which is able to adhere the cord to a rubber or thermoplastic matrix.
 5. A method of manufacturing a transmission belt wherein the cord of claim 4 is adhered to a rubber or thermoplastic matrix and further processed according to methods known for making transmission belts. 